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Summary:? I’m asking for troubleshooting ideas for a 12V Rev2 high bands QMX with 0W transmit output.

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Details:

The QMX rev 2 high bands kit went together very smoothly.

I went over it with a magnifier several times.

Firmware 1_00_14 loaded just fine.

I hear lots of CW and FT8 signals on the receiver when hooked up to an antenna.

The audio, image, and RF sweeps all look close enough to those in the operating manual.

The values in the diagnostics screen all look good (except Power and SWR).

TX power out is 0W and (consequently, I think) the SWR sweeps are bad.

The rig draws 30mA at the power supply on receive and 50mA on transmit.

Vdd measures 5.02V and Vcc measures 3.30V in both transmit and receive.

I don’t have an oscilloscope so I’m looking for advice on further troubleshooting steps that can be done without a scope.

With all the things that are apparently working right, I really ought to be able to narrow down possible reasons for lack of output.

I’d like to exonerate the entire path used in the RF sweeps and am having trouble identifying it.

I’ve been staring at the transmitter schematic for a while but don’t yet get it.

Does the test stimulus for the RF sweeps come from the line labelled “DAC”?

Does the reference measurement for the RF sweeps come from the line labelled “ADC_PA”?

Does the test measurement for the RF sweeps use “ADC_FWD” or “ADC_REV” (I don’t see any other options)?

If those three hypotheses are correct then it seems the only parts not involved in the RF sweeps are IC501-IC503, Q503-Q506, D503-D504, and the BNC connector.

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Does this reasoning make sense?

Are there any tests that can be done with a voltmeter/ohmmeter (no oscilloscope) to get a better clue?
(BTW, diode orientations are all correct).

I’m reluctant to just start pulling components unnecessarily due to the risk of accidentally lifting traces and otherwise damaging the board.

Thanks!

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73, Mike KK7ER

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I launched down a similar road:?/g/QRPLabs/message/115740

Basically, I shorted one of the leads from T501 with a SMD next to it: they were super close on the PCB. I didn't notice the short even when I used a loupe to examine the board after making each solder connection and again before powering it up the first time.

Powering up with that short in place fried Q507. My fried Q507 left me with 0w output and a constant output voltage. With the power off, there was only 50ohms of resistance across the source and gate pins of Q507.?

I found it, with a little encouragement from the forums, by tracing the circuit with a DVM and making sure I was getting expected values (e.g. across resistors) and continuity (e.g., across coils). Maybe you'll find something similar?

Good luck!

Hi Todd,

Thanks!??Yes, I read your thread hoping to see a similar cause.
But my situation is a little different because I don't have the constant output voltage.
For me the voltage is 0.7V in receive and 10.3V in transmit, just like it is supposed to be.
Assuming I understand it correctly, I don't yet see any reason to begin unsoldering SMD components and measuring resistance.
I'm hoping other experienced troubleshooters will chime in with more ideas.

73, Mike KK7ER

Here, here on not unsoldering (or otherwise removing) components without good cause!

Some measurements can be done in situ.

There are some knowledgeable people around: I hope you get some useful info!

I just had the same exact problem. Voltage was at 0.6V on receive and would jump to 10.7V on transmit. No output on any band and the SWR looked very strange into a dummy load. I found that T507 was missing continuity between one of the pairs. I didn't quite get the enamel off of one side. I checked for continuity every time I soldered any enameled wire, but I must've have been touching it just right when I checked the first time. Hope this helps you fix your problem.

Hello Mike,

Have you tried measuring output on a dummy load and with something else other than the diagnostic screen? I would look closely at T507 (the SWR bridge binocular core) for cold joints, possibly T501 and the output MOSFETs.
Also, 30mA on RX seems quite small, considering that you've installed firmware and RX seems to be working fine. Maybe it's a typo, and it's 300mA on RX and 500mA on TX?
Does it manifest the same way on all bands?

Regards,
YO3GFH
op. Adrian

Chris,

Were your RF sweeps OK before you fixed T507?
I ruled out T507 because my RF sweeps were fine and it seems that either ADC_FWD or ADC_REV are being used to collect the output measurements for the RF sweeps.
If I got that right then T507 is OK since T507 sits between the LPFs and measurement points.
If there was no continuity on T507 then the RF sweeps would be bad.

But at first I thought you meant T501 and that got me thinking.
I had ruled out T501 since the test stimulus (assuming coming from DAC) must pass through T501 to perform the RF sweeps.
But I realized that the RF sweep stimulus may be able to pass through T501 even if one of the primary connections was open (circled below).
They both cannot be open because one of them must serve as the return path for the test signal.

But if one of them is open it would prevent the PA output from entering T501.
That might explain good RF sweeps and 0W TX out.
Life was too busy today for QMX troubleshooting.
But that is what I'm going to check next (unless someone throws cold water on my hot hypotheses).

73, Mike KK7ER

Hi Adrian,

Yes, the power meter on the dummy load also shows 0W.
Hmm... you are right about the current being too low.
I was just reading it off the LED display of my cheap current limited power supply without thinking twice about it.


I must have accidentally reset the current limit.

After setting it properly, now I'm getting 3.5 to 5W out (before tweaking the LPFs).
Go figure.

Thanks for pointing that out!

73, Mike KK7ER

On 05/01/2024 02:41, Mike KK7ER wrote:

it seems that either ADC_FWD or ADC_REV are being used to collect the output measurements for the RF sweeps.

Mike,

I'm not sure where you are.
RF sweep input is from Clk2 via R518.
Goes through selected LPF, Q508 to the RX stages and to IC407.

Your highlights have nothing to do with the sweep path. I'm lost.

73 Alan G4ZFQ

Hi Mike,

My RF sweeps looked fine while I had no output. They could of used a little bit of tweaking to get things perfect, but were useable. Once I fixed the bad solder joint on T507, the output sprang to life and the sweeps didn't change. I did some fine tuning on the coils to dial things in before I put the case back on.

[note:? i deleted my previous reply since it referred to the wrong CLK2 line]

Hi Alan,

> I'm not sure where you are.

Here is where I am:? the QMX is fine.? But I seem to have a defective current limited power supply that cannot hold the current limit that is set on it.? It powers the QMX well enough for the receiver and self tests to work.? But when I transmit, it fails to provide adequate current leading to 0W TX out.? Since I had just built the QMX and since the power supply was commercially made, I trusted the power supply and doubted the QMX. I was wrong.

> RF sweep input is from Clk2 via R518.
> Goes through selected LPF, Q508 to the RX stages and to IC407.
> Your highlights have nothing to do with the sweep path. I'm lost.

Sounds like I’m the one who was lost!

Thanks for clearing that up.

I included the marked up schematic in hopes that someone would confirm or correct my thinking.

You corrected it (I think)!

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So here is what I think you are saying is the path for RF sweeps (assuming LPF2 is engaged):

So good RF sweeps would confirm everything in the highlighted path.
But T507 could have still been bad as Chris pointed out.
And T501 is not involved, either.
Thanks for your help.

73, Mike KK7ER

On 06/01/2024 01:49, Mike KK7ER wrote:

So good RF sweeps would confirm everything in the highlighted path.

Mike,

Yes. This is the RF Filter sweep, shows that the LPF passes RF. The chart mainly shows the BPF characteristic. (Unless the LPF is way out.)

Of course the QMX also has the SWR sweep. Clk2 is connected to the PA, this RF goes through T501, the opposite way through the LPFs and the micro measures the SWR from T507.

73 Alan

I am having similar problems with my build. I checked T507 before building and it was OK, my concern is if the enamel melted in the winding section as I had to apply a bit of heat when soldering the thicker leads. Knowing the BNC output is going to be "shorted"(found out by reading some other threads), I am trying to find out what is the best way to test T507 once it is placed on the board. I checked for solder bridges and around and some of the tips due to close points.

Can someone please help with the following?
- In the T507 diagram below, can someone please help identify A/B/C/D connections? Since I think there is a short in my build, the continuity checks are getting me confused.
- What is a good way to confirm, with continuity test, that I have T507 placed correctly and not shorted to something else?



73, Eduardo - KC8R

Eduardo

I had problems with T507 also and can offer

1.? If you attempted to burn off enamel on the thicker wire ( the primaries ) you probably failed to make a good connection.
? ? ?Those wires require scraping the enamel off because it will not "burn off",
2. After reflowing solder with more heat and longer duration of heat on the thin wires my QMX finally produced output power.
? ? At least one of those joint showed a significant take up of additional solder with a longer duration/higher temperature reflow of
? ?the solder joint,
3. Shorts in the T507 can only be found with it removed from the main board.
4. In checking continuity at solder joints it is important to put the probe on the solder pad and not the wire itself.? Continuity at
? ?the pad is required.? With T507 installed there is a DC short to ground on each of the 8 pads as the schematic shows so a
? ?continuity check provides an invalid result.??

I hope this is of use to you.

Charles
K5KXJ

On Sun, Jan 14, 2024 at 09:55 AM, C R Murrell wrote:

If you attempted to burn off enamel on the thicker wire ( the primaries ) you probably failed to make a good connection.
? ? ?Those wires require scraping the enamel off because it will not "burn off",

With ongoing instances of enameled wire soldering issues being reported, I wonder whether it might be prudent for Hans to begin recommending physical removal in his instructions instead of the burning method, which seems to be hit-and-miss and operator-dependent.?
Perhaps if a skilled assembler does it every day they might get good at enamel-burning, find optimum heat settings, etc., but it often seems to have not worked out well for kit many builders.??
I wonder if any of our amateur repair experts might want to comment on how many of the repaired units they have found with this issue?

K5KXJ's comment regarding probing the pad and not the wire is right on, I've gotten bit with this before.
73, Don N2VGU

Thank you for the response and ideas. I will check again, but based on this my problem may be the enamel, since not all 8 points of T507 are passing the continuity check against each other.?

73, Eduardo - KC8R

Thank you everyone for the tips. I redid the solder on connection C on T507 and voila… no more protection mode. Now to the diag fine tune.?

I appreciate all the support.?

73, Eduardo, KC8R